Method and apparatus for treating wastewater

ABSTRACT

This invention is directed to a wastewater treatment system having a fluidizable media carrying anoxic bacteria in a first treatment zone and a filter membrane positioned in a second treatment zone. A wastewater is contacted with the fluidizable media and further contacted with air and a filter membrane.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Application Ser. No. 60/723,744, entitled “METHOD ANDAPPARATUS FOR TREATING WASTEWATER,” filed on Oct. 5, 2005, which isherein incorporated by reference in its entirety.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to a system and method for treatingwastewater, and more particularly to a wastewater treatment system andmethod utilizing a membrane bioreactor.

2. Discussion of Related Art

The importance of membrane for treatment of waste water is growingrapidly. With the arrival of submerged membrane processes where membranemodules are immersed in a large feed tank and filtrate is collectedtypically through suction applied to the filtrate side of the membrane,membrane bioreactors (MBRs) combining biological and physical processesin one stage promise to be more compact, efficient and economic.Membrane bioreactors are typically sized to accommodate community andlarge-scale sewage treatment, i.e. 160,000 gpd, and 20-40 mgd and more.These large-scale wastewater treatment systems are commonly designed tooperate while attended, have numerous controls, and typically requirechemical addition. A need remains for a simple, robust small scalewastewater treatment systems designed for relatively unattended use,requiring only periodic maintenance.

SUMMARY OF INVENTION

In accordance with one or more embodiments, the invention relates to asystem and method of treating wastewater.

In one embodiment, a wastewater treatment system includes a firsttreatment zone fluidly connected to a second treatment zone. Afluidizable media carrying anoxic bacteria is positioned in the firsttreatment zone, and a membrane module comprising a filter membrane ispositioned in the second treatment zone. The wastewater treatment systemmay also comprise an oxygen depleting zone.

Another embodiment is directed to a method of treating wastewaterincludes contacting a wastewater with an anoxic bacteria immobilized ona fluidized media to produce a first water product. The first waterproduct is contacted with air to from a second water product which ispassed through a filter membrane to produce a concentrated mixed liquorand a filtrate.

Another embodiment is directed to a method of treating a wastewaterincluding passing a wastewater through a fluidized bed carrying anoxicbacteria to produce a first treated wastewater. A portion of the firsttreated wastewater is passed through a filter membrane to produce aconcentrated mixed liquor and a filtrate, which is discharged.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 illustrates a system in accordance with one or more embodimentsof the invention.

FIG. 2 is a flow chart illustrating a process in accordance with one ormore embodiments of the invention.

DETAILED DESCRIPTION

This invention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phraseology and terminology used hereinis for the purpose of description and should not be regarded aslimiting. The use of “including,” “comprising,” or “having,”“containing,” “involving,” and variations thereof herein, is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items.

This invention is directed to wastewater treatment systems utilizingmembrane bioreactors designed to treat wastewater flow of about 10,000gpd or less. In one embodiment the wastewater treatment system isdesigned to treat wastewater flow of about 5,000 gpd. One or moreembodiments are directed to a fluidized bed containing bacterialmicro-organisms in conjunction with an MBR. Some aspects relative to oneor more embodiments also include utilizing an oxygen depletion zone inconjunction with the MBR. “Wastewater,” as used herein, defines a streamof waste from a residential or community source, having pollutants ofbiodegradable material, inorganic or organic compounds capable of beingdecomposed by bacteria, flowing into the wastewater treatment system. Asused herein, a “wastewater treatment system” is a system, typically abiological treatment system, having a biomass population of bacterialmicro-organisms of a diversity of types of bacteria, used to digestbiodegradable material. Notably, the biomass requires an environmentthat provides the proper conditions for growth.

One embodiment of the present invention includes bioreactor having oneor more treatment zones. As used herein, the phrase “treatment zone” isused to denote an individual treatment region. Individual treatmentregions may be housed in a single vessel with one or more compartments.Alternatively, individual treatment regions may be housed in separatevessels, wherein a different treatment is carried out in separatevessels. The treatment zone, i.e. the vessel or compartment, may besized and shaped according to a desired application and volume ofwastewater to be treated.

The wastewater treatment system may comprise a fluidizable media housedin a first treatment zone. The fluidizable media may comprise biomasscarriers designed to immobilize anoxic organisms. The biomass carriersmay be formed of any material suitable to support organisms and toremain fluidized under operating conditions. In one embodiment, thefluidizable media has a specific gravity substantially the same as thatof water. In another embodiment the fluidizable media has a surface areaadequate to allow denitrifying bacteria to grow, which may enhance theefficiency of the anoxic reaction to remove nitrogen.

Any volume of fluidizable media may be utilized within the firsttreatment zone for a particular purpose. For example, a maximum volumeof fluidized media may be used to substantially fill the first treatmentzone, or a lesser volume of fluidized material may be used to fill aportion of the first treatment zone. Without being bound by anyparticular theory, passing wastewater through denitrifying bacteriaimmobilized on the fluidizable media may increase the efficiency of thedenitrification process.

The first treatment zone may also comprise means for maintaining thefluidized media within the first treatment zone during operation. Forexample, a baffle, weir, screen or perforated plate may be used tomaintain the fluidizable media within the first treatment zone.Alternatively, the fluidizable media may be prevented from exiting thefirst treatment zone by establishing fluid counter currents duringoperation so that the fluidizable material remains appropriatelysuspended. In one embodiment, a screen or perforated plate is positionedacross an entire cross sectional area of a vessel or compartment formingthe first treatment zone to maintain the fluidizable media within thefirst treatment zone. The screen or perforated plate may also assist inproviding a substantially uniform density of fluidizable media over theentire cross sectional area of the first treatment zone. One or morescreens or perforated plates may be positioned within the firsttreatment zone to establish one or more fluidized bed regions. Forexample, one screen may be positioned at or near the top of the firsttreatment zone to contain a first fluidizable media region, and a secondscreen may be positioned below the first screen to contain a secondfluidizable media region. The fluidizable media may, but need not be thesame in the separate regions. Similarly, the fluidizable media maysupport the same or different anoxic organisms in the separate regions.

According to one embodiment of the invention, one or more porous orpermeable membranes may be positioned in a second treatment zone. Themembrane may have any configuration suitable for a particular purpose,such as sheet or hollow tube. The membrane may be formed of any material(natural or synthetic) suitable for a particular filtration process. Inone embodiment, the membrane is formed of polymeric hollow fibers.

One or more membranes may be positioned in one or more membrane modules.The membrane modules may have any shape and cross sectional areasuitable for use in a desired application, for example, square,rectangular, or cylindrical. In one embodiment, the membrane modules arerectangular.

According to one embodiment of the invention, one or more membranemodules may be positioned in a second treatment zone in such a way as tobe completely submerged by fluid during operation. For example, themembrane module may be positioned vertically, horizontally, or at anangle within the second treatment zone. Multiple membrane modules may bepositioned adjacent one another, or located at predetermined positionswithin the second treatment zone and may, but need not, be positioned inthe same plane as others or parallel to one another. In one embodiment,hollow fiber membranes may be positioned horizontally within the secondtreatment zone. One or more membrane modules may be mounted directly tothe vessel or compartment which forms the second treatment zone.Alternatively, one or more membrane modules may be mounted to a modulesupport which may be removably attached to the vessel or compartmentforming the second treatment zone. In one embodiment, a plurality ofmembrane modules are mounted to a module support rack to facilitatemembrane maintenance and/or replacement. In another embodiment, membranemodules having vertical partitions may be positioned horizontally.

The second treatment zone may include an aeration system to suspendsolids in wastewater or resultant concentrated mixed liquor containedwithin the second treatment zone, and/or to assist water transferthrough the membrane. The aeration system may produce fine bubbles,coarse bubbles, a jet stream of gas, a jet of gas and fluid, andcombinations thereof. The aeration system may be positioned in anysuitable location within the second treatment zone. In one embodiment,aeration may be provided along a length of one or more membrane moduleshorizontally positioned.

The wastewater treatment system may comprise an oxygen depletioncompartment fluidly connected to the first treatment zone and the secondtreatment zone. The oxygen depletion compartment may be sized to accepta portion of a wastestream exiting the first treatment zone, as well asa concentrated mixed liquor from the second treatment zone.

According to another embodiment, the wastewater treatment system maycomprise one or more pretreatment units, such as to collect solidsand/or to remove phosphorous. In one embodiment the pretreatment unit isa trap to remove floating solids, such as grease, and other grossorganic solids until they become more soluble, and is positionedupstream of the first treatment zone. The trap may be sized to provide avolume of about 1×FF (1 forward feed or about 5,000 gpd). In anotherembodiment, the pretreatment unit is a chemical phosphorous removalunit.

According to another embodiment, the wastewater treatment system maycomprise an equalization tank and/or a reserve storage tank fluidlyconnected to the bioreactor. The tank may be sized to accommodatefluctuations in wastewater generation to normalize flow into thebioreactor. For example, the equalization capacity may be equal to about8 hours or about 33% of the FF. The same tank may also be sized toprovide reserve capacity for an emergency such as a power failure, andmay have a reserve capacity of about 16 hours or about 67% of the FF. Inone embodiment, the tank is sized to provide a volume of about 1×FF(about 5,000 gpd) to provide for equalization and a reserve.

Referring to the figures, FIG. 1 illustrates one embodiment of thepresent wastewater treatment system. FIG. 1 shows a bioreactor 10comprising an aerobic compartment 12, an anoxic compartment 14, and anoxygen depletion compartment 16. Two membrane modules 18 are positionedin the aerobic compartment 12. A high level sensor 28 in aerobiccompartment 12 indicates that the wastewater in the aerobic compartmentis approaching full volume, and may indicate that one or both of themembrane modules are not functioning properly. High level sensor 28 mayturn off pump 42 in equalization/reserve tank 40 to interrupt wastewaterflow into the bioreactor 10 and sound an alarm. Low level sensor 30 inthe aerobic compartment 12 indicates that the level of wastewater in theaerobic compartment may fall below the plane of the membrane modules 18,and may subsequently expose the membranes to air causing them to dry.Low level sensor 30 may close valve 50 on line 36 to interrupt flow offiltrate leaving the bioreactor.

Also as shown in FIG. 1, fluidized media 20 carrying an immobilizeddenitrifying bacteria is positioned in the anoxic compartment 14 and isprevented from entering the aerobic compartment 12 by screen 22.Wastewater to be treated enters the anoxic compartment 14 through inlet32 and fluidizes the fluidizable media 20 under anoxic conditions. Thewastewater passes up through the fluidized media 20 containingdenitrifying organisms and produces a first treated wastewater. As shownin FIG. 2, a portion of the first treated wastewater passes to theaerobic compartment 12 at about 6×FF (about 30,000 gpd). A secondportion of the first treated wastewater passes to an oxygen depletioncompartment 16 at about 2×FF (about 10,000 gpd).

Blower 26 forces air through a fine bubble or a coarse bubble aerationsystem 34 in the aerobic compartment 12, providing an air scour for themembrane modules 18 and fluid circulation for the aerobic process. Aportion of the first treated wastewater passes through the membranesunder hydrostatic pressure at about 1×FF (5,000 gpd) to produce afiltrate and a concentrated mixed liquor. In FIG. 1, two B30R membranemodules available from US Filter are used. The membrane modules may beoriented vertically, horizontally, or at a predetermined angle. Themodules may be assembled to a removable rack that can be lifted from thetop of the aerobic compartment 12. A filtrate header (not shown)connects one end of the two membrane modules to line 36. The filtrateexits the first compartment 12 through line 36 for further treatment orrelease.

The concentrated mixed liquor passes to an oxygen depletion compartment16 at about 5×FF (25,000 gpd). Dissolved oxygen is removed form theconcentrated mixed liquor in the oxygen depletion compartment. Theconcentrated mixed liquor combines with a portion of the first treatedwastewater in the oxygen depletion compartment 16 to produce a secondarywastewater. Pump 24 pumps the secondary wastewater at about 7×FF (35,000gpd) to a distribution manifold at the bottom of the anoxic compartment14 for further treatment. As shown in FIG. 2, discharge from pump 24 mayinclude a manifold distribution system 36 to provide a more uniformdistribution of upward flow of wastewater and secondary wastewater inthe anoxic compartment, thereby ensuring the fluidized media remainsfluidized. The manifold distribution system may be sized and shaped toprovide adequate distribution of fluid flow. In one embodiment, themanifold distribution system comprises 1.5 inch pipes with multiple 0.25inch holes to provide uniform distribution of the wastewater andsecondary wastewater up through the fluidized media.

Also illustrated in FIG. 1 are trap 38 and equalization/reserve storagetank 40. Wastewater to be treated enters trap 38 at about 1×FF (5,000gpd) where floating solids are trapped, and inert materials and grossorganic solids settle. The wastewater then flows from trap 38 to tank 40by gravity. Tank 40 has a volume of about 1×FF (5,000 gpd) to equalizeflow and provide a reserve. Pump 42 moves the wastewater at about 1×FF(5,000 gpd) to the anoxic compartment 14. Pump 42 may be any pumpsuitable for the capacity of wastewater to be treated. In oneembodiment, pump 42 may be a Zoller 5040 Filtered STEP System. Tank 40includes 3 level sensors/alarms 44, 46, 48. Low level sensor 44 protectsthe pump from running dry, and high level senor 46 activate a timercontrolling an automatic valve 50 on line 36. Alarm level sensor 48activates an alarm system to override the timer and open valve 50.

The flow chart of FIG. 2 illustrate one embodiment of forward feed,however, other forward feeds are contemplated. For example, forward feedfrom the aerobic compartment, to the oxygen depleting compartment may beincreased or decreased depending upon the amount of recirculationdesired, and the amount of forward feed required to fluidize the media.However, it is preferable that the forward feed from the aerobiccompartment to the oxygen depleting compartment not be increased to suchan extent that dissolved oxygen enters the anoxic compartment.Similarly, it is preferable that the forward feed from the oxygendepleting compartment not be increased to such an extent to allowdissolved oxygen to enter the anoxic compartment. However, in someinstances, the addition of some dissolved oxygen may be expected. With amedia in the system, a biofilm may grow on outer and ineteral surface ofthe media. When the biofilm has grown to a particular thickness, forexample, 50 microns, an inner layer of microorganisms may be exposed toan anoxic environment regardless of whether an outer layer ofmicroorganisms is exposed to aerobic conditions, so that denitrificationmay occur in the inner layer of the biofilm. Minimal addition ofdissolved oxygen is contemplated by this invention as long as thedissolved oxygen does not overwhelm the denitrification process.

Having thus described several aspects of at least one embodiment of thisinvention, it should be apparent to those skilled in the art that theforegoing is merely illustrative and not limiting, having been presentedby way of example only. Numerous modification and other embodiments arewithin the scope of the invention. In particular, although manyembodiments presented herein involve specific combinations of methodacts or system elements, it should be understood that those acts andthose elements may be combined in other ways to accomplish the sameobjectives.

Further, acts, elements, and features discusses only in connection withone embodiment are not intended to be excluded from a similar role inother embodiments.

It is to be appreciated that various alterations, modifications, andimprovements can readily occur to those skilled in the art ant that suchalterations, modifications, and improvements are intended to be part ofthe disclosure and within the spirit and scope of the invention.

Moreover, it should also be appreciated that the invention is directedto each feature, system, subsystem, or technique described herein andany combination of two or more features, systems, subsystems, and/ormethod, if such features, systems, subsystems, and techniques are notmutually inconsistent, is considered to be within the scope of theinvention as embodied in the claims.

Use of ordinal terms such as “first,” “second,” “third,” and the like inthe claims to modify a claim element does not by itself connote anypriority, precedence, or order of one claimed element over another orthe temporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

Those skilled in the art should appreciate that the parameters andconfiguration described herein are exemplary and that actual parametersand/or configurations will depend on the specific application in whichthe systems and techniques of the invention are used. Those skilled inthe art should also recognize or be able to ascertain, using no morethan routing experimentation, equivalents to the specific embodiments ofthe invention. It is therefore to be understood that the embodimentsdescribed herein are presented by way of example only and that, withinthe scope of the appended claims and equivalents thereto; the inventionmy be practice otherwise than as specifically described.

1. A wastewater treatment system comprising: a first treatment zonefluidly connected to a second treatment zone; a fluidizable mediacarrying bacteria positioned in the first treatment zone; and a membranemodule comprising a filter membrane positioned in the second treatmentzone.
 2. The wastewater treatment system of claim 1, further comprising:an oxygen depleting zone fluidly connected to the first treatment zoneand the second treatment zone.
 3. The wastewater treatment system ofclaim 2, further comprising an equalization tank positioned upstream ofthe first treatment zone.
 4. The wastewater treatment system of claim 3,further comprising a pretreatment unit positioned upstream of theequalization tank.
 5. The wastewater treatment system of claim 4,wherein the pretreatment unit is a trap.
 6. The wastewater treatmentsystem of claim 1, wherein the membrane module is disposed at any anglein the second treatment zone.
 7. The wastewater treatment system ofclaim 6, wherein the module is disposed horizontally in the secondtreatment zone.
 8. The wastewater treatment system of claim 1, whereinthe first treatment zone is an anoxic zone.
 9. The wastewater treatmentsystem of claim 8, wherein the second treatment zone is an aerobic zone.10. The wastewater treatment system of claim 1, further comprising meansfor fluidizing the fluidizable media.
 11. The wastewater treatmentsystem of claim 10, wherein the means for fluidizing the fluidizablemedia comprises a manifold positioned in the first compartment below thefluidizable media.
 12. The wastewater treatment system of claim 10,further comprising means for maintaining the fluidizable media withinthe first treatment zone.
 13. A method of treating wastewatercomprising: contacting a wastewater with anoxic bacteria immobilized ona fluidized media to produce a first water product; contacting the firstwater product with air to form a second water product; and passing thesecond water product through a filter membrane to produce a concentratedmixed liquor and a filtrate.
 14. The method of treating wastewater ofclaim 13, further comprising removing at least a portion of dissolvedoxygen from the concentrated mixed liquor.
 15. The method of treatingwastewater of claim 14, further comprising contacting a portion of thefirst water product with the concentrated mixed liquor to form asecondary wastewater.
 16. The method of treating wastewater of claim 15,further comprising contacting a portion of the secondary wastewater withthe anoxic bacteria fixed on the fluidized media.
 17. A method oftreating wastewater comprising: passing a wastewater through a fluidizedmedia carrying anoxic bacteria to produce a first treated wastewater;passing a first portion of the first treated wastewater through amembrane module comprising a filter membrane to produce a concentratedmixed liquor and a filtrate; and discharging the filtrate.
 18. Themethod of treating wastewater of claim 17, further comprising removingat least a portion of dissolved oxygen from the concentrated mixedliquor.
 19. The method of treating wastewater of claim 18, furthercomprising combining a second portion of the first treated wastewaterwith the concentrated mixed liquor to form a secondary wastewater. 20.The method of treating wastewater of claim 19, further comprisingpassing a portion of the secondary wastewater through the fluidizedmedia.
 21. The method of treating wastewater of claim 19, whereinpassing the first portion of the first treated wastewater through themembrane module occurs under hydrostatic pressure.